A refrigeration system of the type used for cooling the air within an enclosure comprises a refrigerant circuit including in-closed series connection, a condenser, flow restricting means, an evaporator and a compressor. The compressor withdraws low pressure refrigerant vapor from the evaporator and discharges high pressure refrigerant to the condenser. A flow restrictor, generally known as a capillary tube, provides a simple and low-cost means for controlling or restricting the refrigerant flow so as to maintain a pressure difference between the condenser and evaporator. However, since a capillary tube provides a substantially fixed-flow restriction, it has only one ideal operating condition. In effect, a simple refrigerant circuit, including a capillary tube restrictor, will operate with maximum efficiency within a relatively narrow range of temperatures and pressures determined by the system design and refrigerant charge. In order to provide a more efficient operation of a refrigeration system under a wide range of operating conditions, it is desirable to provide means for modifying or changing the circulating refrigerant charge, depending upon the operating conditions. One means for accomplishing this comprises a dead-end storage receptacle which is heat exchanged with a portion of the refrigerant circuit between the evaporator and the compressor and which is connected by a two-way flow connection to a portion of the refrigerant circuit which operates at substantially the same pressure as the evaporator. Refrigerant is withdrawn from or added to the circuit by a modulating means in accordance with changes in system pressure and temperature conditions of the portions of the system with which the receptacle is associated.
While the use of modulating and storage means has been effective in controlling system efficiency, this does not solve the problem of compressor overload. When ambient temperatures surrounding the condenser and evaporator increase in a cooling system, the power consumption and bearing load increase because of an increase both in evaporator pressure and of condenser pressure.
One attempt at solving the problem of compressor overload is disclosed in U.S. Pat. No. 3,014,352-Leimbach. In this teaching, when the head pressure exceeds a predetermined amount, a valve tends to open and, upon sufficient head pressure increase, the valve opens completely, thus allowing refrigerant to flow from the high pressure liquid line directly into the suction line, by-passing the evaporator.